Air Pollution Ups Risk Of Stroke, Impaired Memory

This is SCIENCE FRIDAY. I'm Ira Flatow. You probably know that smog is bad for you, or you could just feel it. But the effects of air pollution can go way beyond damaging your lungs, right to your brain, possibly speeding up memory loss, sort of making your brain age faster or upping your risk of stroke if you're out on an especially smoggy day. That's the conclusion of two studies published this week in the Archives of Internal Medicine. Jennifer Weuve is an assistant professor of medicine at Rush Institute for Healthy Aging at Rush University Medical Center in Chicago. She's one of the study authors. And she joins us. Welcome to SCIENCE FRIDAY, Dr. Weuve.

DR. JENNIFER WEUVE: Thank you so much. Good afternoon, Ira.

FLATOW: I can't believe the conclusion that the - that smog is also bad for your brain?

WEUVE: Yeah. It's sort of surprising, isn't it?

FLATOW: Yeah. How does that mechanism work?

WEUVE: Right. Yeah. You know, our study wasn't really designed to examine the mechanism closely, but we have two mechanisms in mind. One is this intriguing evidence - actually, it's pretty much conclusive now - that exposure to particulate air pollution is associated with cardiovascular disease risk. And that risk itself may have a role in affecting cognitive decline and dementia. The second mechanism we're interested in is a little bit more direct. Several studies have found that some of these particles that are in the air, like what we see in smoke and smog and maybe particles we can't even see, that some of these particles can actually get into the brain.

And once they're there, they can cause inflammation, which may be involved in the pathogenesis or progression of dementia. And these particles might even trigger some of those microscopic changes, like the deposition of beta amyloid plaques that are typical of Alzheimer's disease.

FLATOW: Wow. And how do they get into your brain from your nose or your lungs?

(SOUNDBITE OF LAUGHTER)

WEUVE: Sure. I think that's a legitimate question.

FLATOW: Yeah.

WEUVE: Sure. They may get there in a couple of ways, and it sort of depends on how large or small they are. Particles can get into our body, obviously, through inhalation, and some of those particles may go down to the lung where they can cross the barrier between the lung and the blood and enter circulation and then, from there, make their way up into the brain. Some small particles can, literally, go from the nasal passage, attach to the olfactory nerve ending in the nasal passage, travel up the axon and get into the brain that way. Not all particles can do that, but there is some pretty convincing animal evidence that that is certainly possible.

FLATOW: Your studies did not - as you say, you did not study the mechanism of how this is happening...

WEUVE: No.

FLATOW: ...but you studied the statistical correlation.

WEUVE: Yes, we sure did.

FLATOW: And tell us - give us some of the thumbnails that you discovered there.

WEUVE: Yeah, yeah, sure. So kind of starting from the overview level, our study explored exposure to particulate air pollution over the long term, over many years and how that relates to decline in cognitive functioning among older women. And we've already talked about particulate air pollution, and so I'm going to move on a little bit. The most important finding of our study is that women who were exposed to higher levels of particulate matter in the air over the long term experienced more decline in their cognitive functioning over the four years that we evaluated them.

This was true, interestingly enough, for two kinds of particulate air pollution that we studied. One is a smaller called - a form of particle called fine particulate matter, and that's - those are particles that are less than 2.5 microns in diameter, which is one-thirtieth the width of a human hair. That wasn't so surprising to us. Although we certainly - it was nice to see it in the data. What was surprising to us is that we also saw this association with what's called coarse particulate pollution. And those coarse particles are a little bigger. They're 2.5 to 10 microns in diameter - certainly not golf-ball size...

(SOUNDBITE OF LAUGHTER)

WEUVE: ...by any stretch - but we were surprised to see an association with exposure to this form of particulate air pollution as well. But I just want to say that exposure to these two kinds of particulate air pollutions are not always correlated with each other. So just because a person is exposed to a high level of fine particulate matter doesn't mean that they're also exposed to high levels of coarse particulate matter.

FLATOW: And where - what would be the source of the particulate matter? Is it soot? Is it exhaust? Is it smokestacks? Or all of those?

WEUVE: Clearly, you've been studying this. Yeah. Sure. Essentially from burning things. It could be a burning wood. It could be burning fuels, burning coal, another source of dust, however - or of particles is dust, and that dust can come from agricultural sources. It can come from forest fires, and it can also come from industrial processes such as crushing or grinding operations, which is also how we get dust in rural areas when we think of trucks going up gravel roads.

FLATOW: Now, is this a lifelong exposure, or could you be on a really dusty road or in, you know, heavy smog one day and that really will have an effect on you too?

(SOUNDBITE OF LAUGHTER)

WEUVE: Right. You know, we weren't really able to explore that in our study because of how it was designed. However, the study of ischemic stroke looked at that much more directly, and, in fact, that's what makes these two studies very complementary. Essentially, they were looking at the acute effects of being exposed to high-particle days and found that if you were exposed to a day of high air pollution - and we're talking about high air pollution - it wasn't even that high, it's just higher than low.

(SOUNDBITE OF LAUGHTER)

WEUVE: Then you are at higher risk of ischemic stroke. And certainly, we think of stroke or this sort of cerebral vascular disease processes being important and highly relevant to the process of cognitive decline, but we were more interested in these long accruals of exposure.

FLATOW: So does that mean that you think there might be - as where the population is aging and we're able to better diagnose, you know, having mental diseases that would - that air pollution might have something to do with it more than we think it might?

WEUVE: Well, I think it's probably helpful to put our results in perspective. We - the way that we reported our results is we reported the difference in the rate of cognitive decline over time for each additional 10 micrograms per liters cubed increment in particulate matter especially. Now, that sounds really fancy. It's - the difference is if as if you were comparing the average exposure in Boston to Chicago, for example. Certainly, not every place in Boston is the same, not every place in Chicago is the same, and not everyday is the same, but that kind of gives you a sense of the difference we're talking about.

So if we took two women in our study who are alike in every single way except that one had an exposure to particular matter, air pollution, that was 10 units higher than the other, it was as if that higher exposed woman was two years older at her baseline cognitive assessment. So we're talking, you know, kind of in the order aging two years with this higher exposure. Now, that doesn't seem like much on an individual basis. You wouldn't go to your doctor and, you know, be evaluated and your doctor would not frown at you and say, oh, no. You are acting two years older.

(SOUNDBITE OF LAUGHTER)

WEUVE: And you should be if - well, if you're a four-year-old, that might be a problem.

FLATOW: Right.

WEUVE: But if you're a 71-year-old, it wouldn't be a big deal. But, you know, it's helpful to think about this on a population basis, and these results, if they are valid and, you know, they are confirmed in other studies, they could be important. Imagine that we successfully reduce everyone's exposures to particulate matter air pollution - now, there will be some people who are at zero, but most of us have a pretty measurable level of exposure. And now that means that these people will experience slower cognitive decline over time, meaning that fewer people will reach their threshold of dementia during their lives, and affiliated families in society will bear less of a burden due to this condition.

So that's nice, but we can put this in a more quantified perspective. And based on the work of some other scientists who about over 10 years ago made this really interesting forecast, which is that if we had an intervention that we could apply to everyone, say, through air pollution policy, for example, and that this intervention delays the onset of Alzheimer's disease, the most common type of dementia, by two years, we could reduce the number of cases in the United States of dementia. (Unintelligible) dementia, but we can reduce the number of cases of dementia in the United States...

FLATOW: We get it.

WEUVE: ...by about 2 million people over the coming 40 years.

FLATOW: Wow. Wow.

WEUVE: So we're talking about interventions that have a big effect overall, even if we can't see them on an individual.

FLATOW: Well, one last question.

WEUVE: Sure.

FLATOW: In your consideration of particles, can you move nanoparticles into this?

WEUVE: Yeah. You know, that's a great question and certainly relevant to the increase use of nanoparticles in manufacturing and in our personal care products, as well. Well, yeah, what we're - we have a follow-up study to examine exposure to what's called black carbon. These are the particles that are - that can consist of carbon, obviously, but generally they're smaller, and they're emitted through the burning of diesel fuel. And we're certainly interested to see what those look like, and it's certainly one of many future areas for exploration.

FLATOW: Mm-hmm. Well, thank you very much for taking time to be with us today. And, you know, we're certainly going to look for nanoparticles because, as you say, they're ubiquitous. They're everywhere and that's something, I think, you have to include somewhere along the line.

WEUVE: Yes, the trick will be measuring.

(SOUNDBITE OF LAUGHTER)

FLATOW: Yeah.

WEUVE: So wish us luck on that.

FLATOW: Well, details, details, right?

WEUVE: Yes, exactly. Thank you so much.

FLATOW: Thank you very much, Dr. Weuve. Jennifer Weuve is assistant professor of medicine at the Rush Institute for Healthy Aging at Rush University Medical Center in Chicago. Transcript provided by NPR, Copyright NPR.